Rubber is an elastic polymeric substance, and is classified as one of thermoplastic elastomers (TPEs). Rubbers have been distinguished from other resins and polymer oils in physical and chemical properties. Diene rubber is one kind of rubber in which main chains have double bonds. Diene rubber generally requires to be vulcanized in practice.
Vulcanization is a process to convert or modify a raw diene rubber substance. Vulcanization processes use some vulcanizing agents and/or heating to create a strong bond or cross-linking between chain molecules in the diene rubber. Vulcanization processes modify raw diene rubbers to increase some mechanical properties such as elasticity and tensile strength, and to reduce plastic flow. Vulcanization can also prevent diene rubber from swelling at least in some extent.
Sulfur has been used as the most popular vulcanizing agent in the art of rubber manufacturing for many decades and centuries. Sulfur-based vulcanizing agents, such as sulfur powder (S8), however need a higher temperature and a longer time period to promote vulcanization process in a raw diene rubber.
Conventional raw diene rubber compositions generally require a relatively large amount of sulfur-based vulcanizing agent to vulcanize, and then the final rubber would be colored or tarnished by the sulfur. The resulted rubber composition which contains a large amount of sulfur would have a bad haze or yellowing.
It has been also known that sulfur as a vulcanizing agent sometimes leads to a blooming on the surface of rubber in a storage. The blooming phenomenon may pollute an ambient environment around a rubber storage container or tank. In addition, sulfur content level of a conventional rubber article may not meet with industrial or environmental standards among various countries and prefectures. A large amount of sulfur also causes an malodor.
There have been in the art some studies about peroxide for rubber vulcanizations to reduce or terminate the amount of sulfur used to lighten the toxic or harmful effect of sulfur.
Patent Document 1 (JPH04275352A filed by NOF Corp.) discloses a conventional vulcanization process for ethylene propylene rubbers (EPRs) using peroxy monocarbonate.
Patent Document 2 (JPS4615420B filed by Nippon Kayaku) discloses a conventional vulcanization process for EPDM using peroxy carbonate.
Patent Document 3 (JPH04293946A) and Patent Document 4 (JPH06100741A), filed by JSR, disclose some conventional EPR compositions subjected to vulcanization using dicumylperoxide.